Arc-resistant switchgear enclosures must be designed to withstand the pressures and temperatures of gases associated with an internal arcing fault. Such enclosures are designed to direct pressure and hot arc gases away from personnel and to thereby enhance safety. Prior to the present invention, the most commonly employed method of improving switchgear safety through arc-resistant construction was to provide a direct, vertical exhaust vent from each compartment to the top of the switchgear enclosure. A problem with this practice is that it precludes the use of vertically stacked arrangements (e.g., 2-high breaker enclosures, 1-high breaker with voltage transformer drawers, etc.), which are commonly employed in the North American switchgear market. This limitation, i.e., the preclusion of the use of vertically stacked arrangements, limits the commercial acceptance of existing arc-resistant construction in the United States.
Other prior art switchgear designs have employed external arc chambers. A problem with external arc chambers is that they limit the number and type of the switchgear configurations that may be deployed within a given volume.
Furthermore, certain classes of arc-resistant switchgear also require that the pressure and hot arc gases not enter any adjacent enclosures. This provides a problem for ventilating lower mounted compartments of higher ratings, since there may be a requirement for a natural air circulation ventilation path while preventing any pressure and arc gases from entering these ventilated compartments. Typically, any such ventilation system must also allow for proper venting of arc gases if originated in the ventilated compartment.
Further background information relating to the present invention can be found in the following publications:
"The Safety Benefits of Arc Resistant Metalclad Medium Voltage Switchgear," 94-CH3451-2/94/0000-0309, 1994 IEEE;
"Procedure for Testing the Resistance of Metalclad Switchgear Under Conditions of Arcing Due to Conditions of Internal Fault," EEMAC Standard G14-1, 1987 (this is the test standard used in North America; ANSI does not presently address this issue, although an ANSI working committee has been established); and
"Improved Switchgear Safety Through Arc-Resistant Construction," by Paul Thompson and E. John Saleeby, 1994 (presented at the 1994 Electric Utility Conference).